490 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



infer either that the Pacific and the middle Atlantic were in free com- 

 munication during the lower Cambrian or that such communication 

 occurred in some pre-Cambrian time, and that the Atlantic oUenelli are 

 descendants of some Pacific emigrant of that time. All things consid- 

 ered, the latter inference seems the more probable. Certainly the specific 

 development of the Pacific lower and middle Cambrian faunas is quite 

 distinct from that of the contemporaneous Gulf of Mexico faunas, as ex- 

 pressed in the Appalachian phases, and those of the northern Atlantic as 

 preserved in the corresponding Cambrian sediments in the St. Lawrence 

 region and in western Europe. 



Neither the Pacific nor the north middle Atlantic and Arctic Ozarkian 

 faunas are well known, so that their relation to the Gulf of Mexico 

 faunas, which invaded the Mississippi and Appalachian valleys at this 

 time, can not be accurately determined. Of the Canadian /faunas 

 recognized in America, the far western (presumably Pacific) facies agrees 

 much better with the Saint Lawrence and northern Appalachian phase 

 than with that of the Gulf of Mexico as developed in the Mississippi 

 Valley and in the southern Appalachian region. Essentially the same 

 geographic affiliations are indicated by the early and middle Ordovician 

 faunas. 



It is of interest to note that in both the Canadian and the early Ordo- 

 vician the Pacific faunas at times invaded as far east as the Arbuckle 

 uplift in central Oklahoma, and that the faunas of these ages on the south 

 side of Ozarkia and in the Mississippi Valley generally are almost entirely 

 distinct from the Pacific facies in Oklahoma. The conviction that a land 

 barrier (Tahlequah axis) separated Oklahoma and Arkansas is forced on 

 us when we consider that while certain Canadian faunas in these two areas 

 contain very few species in common, a large proportion of those found in 

 Oklahoma is comparable or identical with species occurring in the Saint 

 Lawrence Valley and Newfoundland. How these and other Newfoundland 

 faunas got to Oklahoma, except by way of the Arctic and the Pacific, I 

 can not conceive. To bring them there by the more direct and much 

 shorter Atlantic route we must assume either that they crossed the path 

 of the Gulf of Mexico faunas which, according to present correlations, 

 were entering the Mississippi embayment at these times, or that the Gulf 

 fauna was entirely displaced at such times by the Newfoundland fauna. 

 The latter alternatives seem so improbable that I can not admit either at 

 the present time. 



The Silurian Pacific fauna is practically unknown. Eegarding the 

 Devonian, the record seems very full in the matter of deposits, but less 

 so with respect to the faunas. So far as they go, rather free communica- 



